Bleaching compositions comprising a solid, substantially water-insoluble organic peroxy acid stably suspended in an aqueous medium are generally known from British Patent Specification 1,535,804. It claims fabric bleaching compositions having a viscosity from 200 to 100,000 cp. and a non-alkaline pH, the compositions comprising an aqueous carrier, 1-40 weight % particulate organic substantially water-insoluble peroxygen compound and a thickening agent. Specifically mentioned thickening agents are inorganic thickeners, such as clays, and organic thickeners, such as water-soluble gums, mucilaginous materials starches, polyacrylamides and carboxylpolymethylene. In particular, British Patent Specification 1,535,804 discloses the use of cellulose derivatives such as carboxymethyl celluloses, hydroxypropyl cellulose and methyl hydroxybutyl cellulose, hydrolyzed proteins such as hydrolyzed keratins, glutens, polyvinyl alcohol and polyvinylpyrrolidone and natural gums such as gum arabic, carrageen and various agars.
Further, the non-prepublished European Patent Application No 283,792 discloses storage-stable, pourable aqueous bleach suspensions having a pH value in the range of 1 to 6 and containing (a) particulate, water-insoluble peroxy-carboxylic acid (e.g., diperoxydodecanedioic acid), (b) xanthan gum or agars, (c) hydratable neutral salt (e g., Na.sub.2 SO.sub.4), (d) optionally an acid for pH regulation (e.g . H.sub.2 SO.sub.4), and (e) aqueous liquid.
It is known to be advantageous to use liquid bleaching compositions rather than solid bleaching compositions in automatic clothes washers and dryers. Among those advantages is that with liquid bleaching compositions there is no need for cost-increasing shaping steps, such as granulating and drying. Additionally, liquid bleaching compositions are more easily dispersed in wash liquor or in an automatic clothes dryer so the fabrics are more rapidly and evenly bleached. Uneven bleaching can damage fabric as a result of localized high concentrations of bleaching agent.
As disclosed in European Patent Application 176 124, the bleaching compositions of GB 1 535 804, at least as far as they are pourable, have the disadvantage that they are not physically stable. As shown by Composition 7 in EP 176 124, after prolonged storage, pourable bleaching compositions of GB 1 535 804 undergo phase separation, producing a thick bottom layer which is difficult to disperse or homogenize. Consequently, the aforementioned advantage of even fabric distribution may be partly eliminated.
Further it should be mentioned that GB 1,535,804 does not disclose or suggest the use of more than one thickening agent in a single fabric bleaching composition. Indeed, it is clear from Example III of GB 1,535,804 that the cellulose derivatives tested as thickening agents were tested in individual, separate bleach compositions. Additionally, the bleach composition of Example III of GB 1,535,804 is a "thick, semi-gelatinous composition" (see page 11, lines 32-35 of GB 1,535,804) rather than a pourable composition of the present invention.
It should be noted that U.S. Pat. No. 4,232,141 (NL 707,916) discloses, inter alia, grinding coarser particles of a polymerization initiator in an aqueous medium containing a dispersing agent to form an aqueous dispersion of the polymerization initiator. The polymerization initiator may be, inter alia, a peroxy dicarbonate or a benzoyl peroxide. Claim 9 claims that the dispersing agent may be polyvinyl alcohol, cellulose ether, gelatine or a mixture thereof. However, only single dispersing agents (either polyvinyl alcohol or methyl cellulose) are used in the working examples of U.S Pat. No. 4,232,141 to form polymerization initiator dispersions. These dispersions were then added to vinyl chloride polymerization suspensions to form polyvinyl chloride. Some vinyl chloride polymerization suspensions of the examples of U.S. Pat. No. 4,232,141 contain a mixture of polyvinyl alcohol and methyl cellulose. However, as demonstrated herein below, an aqueous suspension acceptable under bleaching conditions (pourability, physical stability and chemical stability) and prepared as suggested by U.S. Pat. No. 4,232,141 is not physically stable.
Further, the product brochure "Xanthan Gum/Keltrol/Kelzan/a natural biopolysaccharide for scientific water control" (printed by Kelco, a division of Merck & Co., Inc 1976, Second Edition) teaches at pages 8 and 9 that "[x]anthan gum is compatible with most commercially available thickeners, both synthetic and natural". However, the brochure also teaches that "[t]he use of xanthan gum with cellulose derivatives is generally not recommended". Thus, the brochure does not mention the use of xanthan gum with polyvinyl alcohol and specifically teaches against the use of xanthan gum with cellulose derivatives.
It has been surprisingly found that a pourable bleaching composition may be formed comprising a solid, substantially water-insoluble organic peroxy acid stably suspended in an aqueous medium, the aqueous medium also comprising at least two polymers wherein the first polymer is one or more natural gums, such as xanthan gum, and the second polymer is selected from the group consisting of polyvinyl alcohol ("PVA"), cellulose derivatives and mixtures thereof. The term "mixtures thereof" includes mixtures of only cellulose derivatives as well as mixtures of one or more cellulose derivatives with PVA. The composition may also comprise an electrolyte, such as Na.sub.2 SO.sub.4.
To be useful, the current bleaching compositions should be conveniently pourable and relatively stable, both chemically and physically.
The bleaching compositions of the current invention are conveniently pourable when they may be poured relatively easily and smoothly from small containers (e g. household size, approx. 0.1 to 2.0 liters) and large containers (e.g. industrial and bulk transport size). Quantifying the "pourability" of the current bleaching compositions is difficult since the compositions are non-Newtonian fluids. With non-Newtonian fluids the shear stress (an indication of a fluid's resistance to flow and therefore its Pourability) varies with the shear rate. For example, some non-Newtonian fluids may have very little initial resistance to flow and pour easily and smoothly. The preferred current bleaching compositions have such flow behavior for both large and small containers. However other non-Newtonian fluids may have substantial initial resistance to flow and then pour easily and smoothly, as with tomato ketchup. Non-Newtonian fluids may also be gel-like and offer both initial and continued resistance to flow. Initial resistance to flow may be referred to as a fluid's "yield value". Generally, bleaching compositions having little or no yield value are preferred; that is, they are conveniently pourable. As one advantage of the current two-polymer bleaching composition, it is possible to prepare stable aqueous suspensions of substantially water-insoluble organic peroxy acid having little yield value. Although viscosity measurements do not precisely measure either the pourability or the yield value of non-Newtonian fluids, viscosity measurements do indicate the relative thickness and thus the relative pourability of non-Newtonian fluids. The Brookfield method is one well-known way to measure the viscosity of a fluid. However, the Brookfield method does not measure shear rate. Since the viscosity of a non-Newtonian fluid is shear rate-dependent, Brookfield viscosity provides only a relative indication of the viscosity of a fluid. In general, though non-limiting, bleaching compositions of the current invention are "pourable" if the Brookfield viscosity is below about 2000 mPa.s (Brookfield 20 r.p.m.) and preferably below about 1500 mPa.s (Brookfield, 20 r.p.m.).
On the other hand, with the appropriate equipment (such as a Haake Rotorisco RV 100), it is possible to measure the shear stress and the shear rate of a non-Newtonian fluid. Such data may be used to predict the yield values of such fluids. Further, viscosity may be calculated from the stress and shear rate data. A plot of viscosity versus shear rate data produces a "rheogram". Since the viscosity of a non-Newtonian fluid is shear rate-dependent, a rheogram provides a more accurate viscosity profile and therefore a better indication of the "pourability" of non-Newtonian fluids. The above-referenced product brochure "Xanthan Gum/Keltrol/Kelzan/a natural biopolysaccharide for scientific water control" provides the shear rate values acting on solutions of xanthan gum as they are poured from a bottle over the shear rate range of about 10-100 s.sup.-1 (see page 28).
The bleaching compositions of the current invention are chemically stable when the activity of the organic peroxy acid undergoes insignificant, and preferably no, reduction over a reasonable storage time. One measure of the potential bleaching activity of an organic peroxy acid, or a composition containing an organic peroxy acid, is the active oxygen (A.O.) content. However, "active oxygen" is affected by the presence of H.sub.2 O.sub.2 as well as peroxy acid. Therefore, a more accurate indication of chemical stability after storage is "residual peroxy acid" which is active oxygen minus H.sub.2 O.sub.2.
The bleaching compositions of the current application are physically stable when the compositions undergo insignificant, and preferably no, phase separation during a reasonable storage time.